Capacitive transducer and method of manufacturing same

Abstract

Provided is a capacitive transducer including an element including a plurality of cells supported such that a vibrating membrane including one of a pair of electrodes formed with an gap inbetween is capable of vibration, wherein a distance between a pair of electrodes of a cell in an end portion of the element is greater than that between a pair of electrodes of a cell in a middle portion of the element.

What is claimed is: 
     
       1. A capacitive transducer comprising:
 an element including a plurality of cells, the element having an end portion and a middle portion, and having at least one of the cells in the end portion and at least one of the cells in the middle portion; 
 wherein each cell has a first electrode and a second electrode which is included by a vibrating membrane, 
 wherein the first electrode and the second electrode are formed separated by a distance, and 
 wherein a shape of the element is rectangular having a pair of long sides and a pair of short sides, and, in a direction along a long side, the distance between the first electrode and the second electrode in the at least one cell in the end portion is greater than the distance between the first electrode and the second electrode in the at least one cell in the middle portion of the element. 
 
     
     
       2. The capacitive transducer according to  claim 1 , wherein the vibrating membrane of the at least one cell in the end portion has a spring constant that is smaller than the spring constant of the vibrating membrane of the at least one cell in the middle portion. 
     
     
       3. The capacitive transducer according to  claim 1 , wherein, in the element, the at least one cell in the end portion and the at least one cell in the middle portion are structured such that in each cell charges on the electrodes impose an electrostatic force F E  on the vibrating membrane of that cell, and the at least one cell in the end portion and the at least one cell in the middle portion are further structured such that a restoring force F Me  of the vibrating membrane of the at least one cell in the end portion is less than a restoring force F Mm  of the vibrating membrane of the at least one cell in the middle portion by such an amount that a sum F Me +F Ee  of the restoring force and the electrostatic force on the vibrating membrane of the at least one cell in the end portion is equal to the sum F Mm +F Em  of the restoring force and the electrostatic force on the vibrating membrane of the at least one cell in the middle portion, where F Ee  is the electrostatic force of the at least one cell in the end portion and F Em  is the electrostatic force of the at least one cell in the end portion. 
     
     
       4. A probe comprising the capacitive transducer according to  claim 1 . 
     
     
       5. An object information acquiring apparatus comprising:
 the capacitive transducer according to  claim 1 ; and 
 a processing unit in which an electrical signal, output from the capacitive transducer due to an acoustic wave propagated from an object being incident upon the vibrating membrane, is used to acquire characteristic information relating to an inside of the object. 
 
     
     
       6. The object information acquiring apparatus according to  claim 5 , further comprising a transmission unit with which the vibrating membrane is vibrated by applying voltage to the pair of electrodes to cause transmission of an acoustic wave,
 wherein the acoustic wave is a reflection of the transmitted acoustic wave from an inside of the object. 
 
     
     
       7. The object information acquiring apparatus according to  claim 5 , further comprising a light source, wherein the acoustic wave is a photoacoustic wave generated from the object irradiated with light from the light source.